IC card and its manufacturing method

ABSTRACT

An IC card has an IC chip and a circuit layer formed between layers of a base material that are adhered together by an adhesive. The IC card has a thickness of 0.25 to 0.76 mm and therefore the thickness of the IC chip needs to be about 0.2 mm, which requires grinding of the IC chip. In use, the IC card is subject to bending forces which apply a bending stress on the chip. In the process of grinding the IC chip, grinding flaws having sharp parts arise that reduce the bending strength of the chip. Also, during the dicing process of the wafer, chipping occurs that results in notches having sharp tip parts being formed in the chip. The grinding flaws that result from the grinding and the notches that result from the chipping are etched to remove their sharpness, which occurs at the tip part of the grinding flaw or the tip part of the notch. By rounding these sharp parts through the etching step, the bending strength of the IC chip increases and the durability of the IC card is ensured.

BACKGROUND OF THE INVENTION

Recently, demand of an IC card is rising as an electronic approval card,a prepaid card, a periodic ticket and a card for individualcertification and so on.

The IC card has the following feature.

1) The memory capacity of the IC card (500-16000 characters) is greaterthan the memory capacity of a conventional magnetic card (about 80characters).

2) The IC card is harder to forge than the magnetic card.

3) By using the electromagnetic induction phenomenon by radiotransmission, the nontouch type IC card can be manufactured.

Usually, a card( IC card, magnetic card) is put in a purse, a card caseor carried loose; so, the IC card is required to satisfy the followingsame specifications compared to a magnetic card.

1) The size of the IC card is smaller than the magnetic card.

2) The thickness of the IC card is the same or thinner than the magneticcard.

3) The weight of the IC card is the same or lighter than the magneticcard.

4) The IC card is flexible against bending by external force.

The IC card has the IC chip, therefore, the IC card has a possibility ofdamage of the IC chip by the transformation.

The following is important in order to improve the reliability of the ICcard against the transformation.

1) Structure of the IC card that resists the transformation to the ICchip.

2) Structure of the IC chip that even if the IC chip is transformed, theIC chip does not destroy.

The IC card that is hard to transform the IC chip even if the IC card istransformed is disclosed to Japanese patent Laid-open print No.64-11895(prior art 1). Prior art 1 is disclosing the IC card structurethat the IC chip suppresses the transformation by holding andreinforcing the IC chip with a metal plate.

It is important that the IC chip itself should be thin and to decreasethe defect of the IC chip surface so that it is hard to destroy it bythe transformation. A bending transformation of the IC chip and a stressof the IC chip surface are proportional to the thickness of the IC chip.

Generally Silicon (Si) used as a material of the IC chip is a brittlematerial. The IC chip is destroyed from the mirror surface defect. So,it is desirable to decrease the defect of the chip mirror surface.

A method of preventing destruction by forming the IC chip itself isdisclosed to the Japanese patent Laid-open print No. 1-235699(prior art2). Prior art 2 is disclosing the manufacturing method of removing themicro crack on the mirror surface of the IC chip by etching processing.

The Japanese patent Laid-open print No. 4-62921(prior art 3) uses plasmaetching machine and is disclosing a removal of the reaction secondaryproduct by 2 step etching.

The Japanese patent Laid-open print No. 6-232255(prior art 4) is dicinga wafer from the mirror surface of the chip to prevent the chipping thatoccurs in the mirror surface of the chip.

SUMMARY OF THE INVENTION

By the improvement of the manufacturing technique of the IC circuit, thethin type and the small area of the IC chip are advancing recent years.The thin type and the small area of the IC chip improve the flexibilityagainst the transformation of the IC card. But high precision of themanufacture technique of the IC chip is also high is required. Despitethe IC chip becoming thinner than the past and the removal the microcrack in the IC chip by etching before dicing wafer (prior art 2), thestrength improvement of the chip is insufficient. The method of dicingof the wafer from the mirror surface of the chip (like prior art 4)cannot suppress the chipping that occurs in the device surface of thechip. Therefore, the IC chip strength is not improved.

The IC chip after dicing is thin, and the area is small. Therefore, itis difficult to etch only the mirror surface of the IC chip selectivelyby plasma etching, etc. from the problem of productivity and thetransfer. When using isotropical chemical etching, etc., the devicesurface of the IC chip is eroded by etching. The purpose of the presentinvention is to provide an IC card which has high reliability againsttransformation by external force.

The inventors determined a break stress on the mirror surface and thedevice surface of the IC chip by 3 points bending test. The test resultwas analyzed by accumulative probability to destroy and break stress(FIG. 3). FIG. 3 (A) illustrates the break stress of the mirror surfaceof the IC chip. FIG.3 (B) illustrates the break stress of the devicesurface of the IC chip. As is clear from this figure, break stress onthe mirror surface of the IC chip is smaller than break stress on thedevice surface of the IC chip and the dispersion of break stress alsoenlarges.

From this, it is thought that the defect much exists on the mirrorsurface of the IC chip. The inventors measured the break stress on themirror surface of various IC chips for which the grinding conditions atthe time of IC chip manufacturing are the same and dicing conditions aredifferent, by the 3 points bending test. The result was arranged on FIG.4. As it is shown in FIG. 4, dicing conditions (four conditions; DicingA, Dicing B, Dicing C, Dicing D ) also greatly changes break stress ofthe IC chip. It is proved that the defect that arises from this dicingin the manufacturing process of the IC chip has given the break strengthof the IC chip a large influence.

In FIG. 5, the typeof defects on the mirror surface after dicing the ICchip are shown. The circumference part of the chip is inhere many flawsoccur. This is chipping caused on the mirror surface of the IC card bythe process of dicing. From this, the destruction strength of the ICchip declines by the chipping that arises on the mirror surface side bydicing of the manufacturing process of the IC chip.

That is, from the inventor's analysis it is found that elimination ofthe chipping that exists in the circumference part on the mirror surfaceof the IC chip improves the destruction strength of the IC chip. Theprocess of etching the IC chip is done after dicing to eliminate thechipping that occurs on the mirror surface of the IC chip. But the ICchip that is the present application field of the invention has athickness 60 μm or less. The IC chip, after dicing is very thin andsmall so it is difficult to handle. Therefore, there is a problem inproductivity and the transfer by the method of etching only the mirrorsurface selectively by plasma etching machine, etc.

When the IC chip is etched by chemical etching, the problem of the aboveproductivity and the transfer does not arise. But a problem has beendiscovered of eroding the device surface as well as the mirror surfaceof the IC chip by etching because etching cannot be done selectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the sectional view of the IC card that is example of thepresent invention.

FIGS. 2(a) to (f) show part of the manufacturing process of the IC chipthat is the example of the present invention.

FIGS. 3(a) and (b) illustrate relationship found by the inventorsbetween the accumulative probability to destroy and break stress of theIC chip that is used for a conventional IC card.

FIG. 4 illustrates a relationship found by the inventors betweenaccumulative probability to destroy and break stress by dicing conditionof the IC chip that is used for a conventional IC card.

FIG. 5 represents the state of the mirror surface after dicing of the ICchip that is used for a conventional IC card as found by the inventors.

FIG. 6 represents the generation mechanism of the chipping in themanufacturing process of the IC chip as analyzed by the inventors.

FIG. 7 is the figure that shows the difference between the breakingstresses of the IC chip of the present invention and a conventional ICchip.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As follows, the example 1 of the present invention is referred to and isexplained by using the figure. FIG. 1 is a sectional view of the IC cardof this example. The thickness of the IC card of this example is anabout 0.46 mm. Card base material 11 is pasted together by adhesive 12,and IC chip 9 and circuit layer 13 are included. As for IC chip 9, themirror surface and the side are etched.

Because of excluding the sharpness part of chipping 7 that arises in theIC chip by dicing, the IC chip bending strength enlarges. The advantagethat is equal to this example as for the IC card having the thicknessabout 0.46 mm, can be expected for the IC card of thickness 0.76 mm orless.

The manufacturing process of IC chip 9 is explained by using FIG. 2. Inthe manufacturing process of the IC chip, in the process (FIG. 2(a)) ofsupplying the protection agent after the circuit installation process,the epoxy resin is first applied to surface 3 of the device of wafer 1before mirror surface grinding and dicing as protection agent 2. Theprotection agent does not need to be the epoxy resin. It has only to bea material that is not eroded in the etching process (FIG. 2(e)) that isdone later. For example, heat curable resin, thermoplastic resin, etc.are fine. The purpose of applying the protection agent is that itprevents erosion of the device surface of the IC chip by the etchingprocess (FIG. 2(e)). In this example, the protection agent is appliedbefore mirror surface grinding and dicing and after the circuitinstallation. It is contemplated to apply the protection agent aftermirror surface grinding. The time of the protection agent application isbefore dicing process, otherwise it is not limited especially.

The mirror surface grinding process (FIG. 2(b)) is done from the side ofold mirror surface 4 of the wafer. As for the IC card at present, thethickness is 0.76−0.25 mm. In order to store the IC chip in the IC cardof this thickness, the IC chip needs grinding until the thicknessbecomes 0.2 mm. To the IC chip stored in the IC card, it likewise withthe IC card is bent by force that is added from the outside at the timeof carrying the IC card and at the time of using, and the transformationarises and a stress occurs on the surface of the IC chip.

The thickness of the IC chip is defined as T, the Young's modulus rateof the IC chip is defined as E, and radius of curvature of the IC chipis defined as R. The IC chip bending stress σ is represented withσ=ET/(2R).

If the IC chip is thin, the bending stress of the IC chip becomes smallagainst the bending transformation of the IC chip of the same radius ofcurvature. Therefore, as for the IC chip, it is desirable that it isground to lighten as much as possible. Grinding flaw 6 arises in mirrorsurface 5 of wafer 1 at the time of mirror surface grinding.

In the IC chip manufactured by a conventional IC chip manufacturingmethod, it has possibility that it becomes the factor that grinding flaw6 that arises at the time of mirror surface grinding makes it reduce thebending strength of the IC chip. For example, it is desirable reduce thegrinding speed not to be able to do grinding flaw 6 on the mirrorsurface of the IC chip when the mirror surface of the IC chip is ground.But to reduce the grinding speed increases the time that is needed inthe mirror surface grinding in the production process of the IC chip.According to this example, grinding flaw 6 is eliminated in the etchingprocess (FIG. 2(e)). So, grinding flaw 6 that arises at the time ofmirror surface grinding can be permitted and possible to improveproductivity. For example, it is not necessary to reduce the grindingspeed in the method of manufacturing the IC chip that is used for the ICcard of which the thickness is 0.46 mm or more. As for the IC card ofwhich the thickness is 0.46 mm or less, it is desirable that theconventional method of making a grinding flaw small also is done. As aresult the IC chip of which the bending strength is high can bemanufactured. Manufacturing of the IC card of high reliability isenabled.

Dicing process (FIG. 2(c)) of the next ground IC chip is done. Dicinguses the blade of 20 μm thickness here. The protection agent also is cutwith the wafer by dicing process (FIG. 2(c)). There is a fear of theoccurrence of chipping 7 in the circumference part of the IC chip bydicing process (FIG. 2(c)). Chipping generation mechanism is shown inFIG. 6. When blade 10 cuts protection agents 2 and wafer 1, the part ofwafer that is not cut destroys the part from which wafer was cut asstarting point 15. This destruction is called chipping. It is thoughtthat the vibration that is given to wafer 1 by the rotation of blade 10is the cause to this.

FIG. 5 shows the chipping that occurs in the IC chip by dicing. Chipping7 comes to the circumference of the IC chip like a notch. The depth ofchipping 7 is form 10 μM to more than 100 μm. It becomes the cause thatchipping 7 reduces the bending strength of the IC chip. The method ofslowness of the transmission speed of blade 10 in order not to generatethis chipping as much as possible is thought. But this method has thefear of increasing the time that is needed in dicing process. In themethod of manufacturing the IC chip in the example of the presentinvention, coming of the sharp notch of the chipping 7 tip part isremoved in the back etching process (FIG. 2(e)). Therefore, chipping 7that arises at the time of dicing process can be permitted, and it ispossible to improve productivity. The chip after dicing consists like ofFIG. 2(d). Grinding flaw 6 and chipping 7 arise in mirror surface 5 inIC chip 8 after dicing.

Etching processing (FIG. 2(e)) is done. Etching processing is done bychemical etching by the mixture liquid of fluoric acid, nitric acid andacetic acid. As for IC chip 8, the surface without device surface 3(mirror surface 5 and side ) protected by resisting is processed by thisetching. The purpose of etching processing is not to remove all chipping7 that occurs in mirror surface 5 of IC chip 8 and all grinding flaws 6.The purpose of etching processing is to remove sharp notch coming of thechipping tip part or the grinding flaw tip part that gives thedeclination of the bending strength of the IC chip the influence.

As for the etching quantity, the bending strength improvement of the ICchip has the Advantage sufficiently in 10 μm or less. When even if theetching quantity is greatly taken, the problem of erosion of the partdoes not arise other than the mirror surface of the IC chip, if theetching quantity is enlarged, the Advantage of the bending strengthimprovement of the chip also enlarges. After the etching process (FIG.2(e)), the protection agent removal (FIG. 2(f)) is done.

In the process of the protection agent removal, the protection agentapplied on device surface 3 of IC chip 9 is eliminated. The protectionagent removal is chemically done by dipping the IC chip in theprotection agent removal liquid. While acetone was used as a protectionagent removal liquid in this example, the protection agent removalliquid is not limited to this, the protection agent can be removed, anddevice surface 5 of IC chip 8 has only not to be eroded.

FIG. 7 is the result that the bending strength of IC chip 9 of thisexample is measured. The bending strength of the IC chip went by thethree points bending test. For the comparison, the result that thebending strength of the IC chip that does not eliminate the chippingthat occurs in dicing is shown in FIG. 7. As it is shown in FIG. 7, thebending strength of the IC chip of this example becomes 2 times or morevalue of the bending strength of the IC chip manufactured in theconventional method. The method of manufacturing the IC chip by thisexample understands that it is valid for IC chip manufacturing that ishard to be destroyed.

The present invention provides an IC card and its manufacturing methodof high reliability that is hard chip breakage to the IC chip.

What is claimed is:
 1. An IC card, comprising: layers of a base materialsecured together with an adhesive; an IC chip fit between the layers ofthe base material, including: a first surface wherein a circuit isformed on the first surface; a second surface located on a back side ofthe first surface; a third surface located between the first and secondsurfaces, wherein the second surface has grinding flaws and the thirdsurface has chipping flaws that are rounded to remove sharpness byetching said second and third surfaces.
 2. An IC card according to claim1, wherein the IC chip is made of silicon.
 3. An IC card according toclaim 1, wherein the one of grinding and chipping flaws that have beenrounded are located at a circumferential part of the IC chip.
 4. An ICcard according to claim 1, wherein a thickness said IC chip is 0.2 mm orless.
 5. An IC chip manufacturing process, comprising: forming a circuiton a first wafer surface; forming a protection agent over said firstwafer surface; grinding a second wafer surface on a back side of thefirst wafer surface to form a thinner thickness of the wafer than thatof before the grinding; dicing said wafer to form said IC chip, saidwafer having sharp portions on the second surface due to the grinding;etching said IC chip on which said protection agent is formed; removingsaid protection agent from said IC chip, wherein the second wafersurface and a third surface formed by said dicing are etched to formrounded portions from sharp portions on said second surface thatresulted from said grinding and from chipping flaws on said thirdsurface that resulted from said dicing.
 6. An IC chip manufacturingprocess according to claim 5, wherein said grinding of said secondsurface is performed after forming said protection agent over said firstwafer surface, and then said IC chip is subject to said etching stepafter said dicing step.
 7. An IC chip manufacturing process according toclaim 5, wherein said protection agent is formed after said grinding ofsaid second wafer surface and said etching is performed after saiddicing.
 8. An IC card manufacturing process, comprising: forming acircuit on a first wafer surface; forming a protection agent on saidfirst wafer surface; grinding a second wafer surface on a back side ofthe first wafer surface to form a thinner thickness of the wafer thanthat of before the grinding; dicing said wafer to form said IC chip,said wafer having sharp portions on the second surface due to thegrinding etching said IC chip on which said protection agent is formed;and removing said protection agent from said IC chip, wherein the secondsurface and a third surface formed by said dicing are etched to formrounded portions from sharp portions on said second surface that resultfrom said grinding and from chipping flaws on said third surface thatresulted from said dicing; fitting said IC chip between base layers ofsaid card and securing said layers together with an adhesive.
 9. An ICcard manufacturing process according to claim 8, wherein said grindingof said second surface is performed after forming said protection agentover said first wafer surface, and then said IC chip is subject toetching after said dicing step.
 10. An IC chip manufacturing processaccording to claim 8, wherein said protection agent is formed after saidgrinding of said second wafer surface and said etching is performedafter said dicing step.
 11. A method of manufacturing an IC cardaccording to claim 8, wherein said etching includes wet chemical etchingwith a liquid mixture.
 12. A method of manufacturing an IC cardaccording to claim 8, wherein said etching includes etching with aliquid mixture comprising fluoride acid, nitric acid and acetic acid.